Controlled engine exhaust gas recirculation is a commonly used technique for reducing oxides of nitrogen in products of combustion that are exhausted from an internal combustion engine to atmosphere. A typical EGR system comprises an EGR valve that is controlled in accordance with engine operating conditions to regulate the amount of engine exhaust gas that is recirculated to the induction fuel-air flow entering the engine for combustion so as to limit the combustion temperature and hence reduce the formation of oxides of nitrogen.
Since they are typically engine-mounted, EGR valves are subject to a harsh operating environment that includes wide temperature extremes and vibrations. Exhaust emission requirements impose more stringent demands for improved control of such valves. Use of an electric actuator is one means for obtaining improved control, but in order to be commercially successful, such an actuator must be able to operate properly in such extreme environments for an extended period of usage. Moreover, in mass-production automotive vehicle applications, component cost-effectiveness is also essential. An EGR valve electric actuator that possesses more accurate and quicker response results in improved driveability and fuel economy for a vehicle having an internal combustion engine that is equipped with an EGR system. It also provides better control over tailpipe emissions.
The present invention relates to new and unique construction for certain component parts of such a valve that enables accuracy and response to be improved, and also better ambient cooling to be achieved while, providing a means to resist intrusion of foreign matter, such as muddy water for example, into the internal valve mechanism via the improved ambient cooling means.
Certain aspects of the invention relate to improvements in certain parts of the valve that provide for a more accurate definition of the magnetic circuit air gap that is provided by upper and lower stator members. Better concentricity and locating of these two stator members, and other related parts such as a bearing guide member that guides the valve shaft, improve accuracy and response. The manner of uniting certain parts also improves the ruggedness of the valve by ensuring that relative movement of the parts that might change important relationships affecting performance does not occur in use.
The invention also relates to improvements in the area of the valve that contains the lower stator member and the bearing member. Generally speaking, the organization and arrangement of these two members, and some related, parts improves part-to-part concentricity and is useful in resisting intrusion of muddy water into the interior operating mechanism.
The problem of muddy water intrusion arises because of the desirability of providing air ambient circulation through a portion of the valve. The pintle head and associated valve seat are in the hot exhaust path through the valve and are exposed to very high temperatures. The electric actuator is operatively connected to the pintle, but is slightly farther away from the engine. It is desirable to provide for air circulation through the valve housing between the actuator and the parts that are closer to the engine. However since it is engine-mounted, the valve will be subject to the outside environment, and one of the hazards is muddy water intrusion due to road splash, etc.
Various features, advantages, and benefits of the invention for achieving the desired objectives will be seen in the ensuing description and claims that are accompanied by drawings. The drawings disclose a presently preferred embodiment of the invention according to the best mode contemplated at this time for carrying out the invention.